1 //! See Rustc Dev Guide chapters on [trait-resolution] and [trait-specialization] for more info on
4 //! [trait-resolution]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html
5 //! [trait-specialization]: https://rustc-dev-guide.rust-lang.org/traits/specialization.html
7 use crate::infer::outlives::env::OutlivesEnvironment;
8 use crate::infer::{CombinedSnapshot, InferOk, RegionckMode};
9 use crate::traits::select::IntercrateAmbiguityCause;
10 use crate::traits::util::impl_trait_ref_and_oblig;
11 use crate::traits::SkipLeakCheck;
13 self, FulfillmentContext, Normalized, Obligation, ObligationCause, PredicateObligation,
14 PredicateObligations, SelectionContext,
16 //use rustc_data_structures::fx::FxHashMap;
17 use rustc_errors::Diagnostic;
18 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
19 use rustc_hir::CRATE_HIR_ID;
20 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
21 use rustc_infer::traits::{util, TraitEngine};
22 use rustc_middle::traits::specialization_graph::OverlapMode;
23 use rustc_middle::ty::fast_reject::{self, TreatParams};
24 use rustc_middle::ty::fold::TypeFoldable;
25 use rustc_middle::ty::subst::Subst;
26 use rustc_middle::ty::{self, Ty, TyCtxt};
27 use rustc_span::symbol::sym;
28 use rustc_span::DUMMY_SP;
31 /// Whether we do the orphan check relative to this crate or
32 /// to some remote crate.
33 #[derive(Copy, Clone, Debug)]
39 #[derive(Debug, Copy, Clone)]
45 pub struct OverlapResult<'tcx> {
46 pub impl_header: ty::ImplHeader<'tcx>,
47 pub intercrate_ambiguity_causes: Vec<IntercrateAmbiguityCause>,
49 /// `true` if the overlap might've been permitted before the shift
51 pub involves_placeholder: bool,
54 pub fn add_placeholder_note(err: &mut Diagnostic) {
56 "this behavior recently changed as a result of a bug fix; \
57 see rust-lang/rust#56105 for details",
61 /// If there are types that satisfy both impls, invokes `on_overlap`
62 /// with a suitably-freshened `ImplHeader` with those types
63 /// substituted. Otherwise, invokes `no_overlap`.
64 #[instrument(skip(tcx, skip_leak_check, on_overlap, no_overlap), level = "debug")]
65 pub fn overlapping_impls<F1, F2, R>(
69 skip_leak_check: SkipLeakCheck,
70 overlap_mode: OverlapMode,
75 F1: FnOnce(OverlapResult<'_>) -> R,
78 // Before doing expensive operations like entering an inference context, do
79 // a quick check via fast_reject to tell if the impl headers could possibly
81 let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
82 let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
84 // Check if any of the input types definitely do not unify.
86 impl1_ref.iter().flat_map(|tref| tref.substs.types()),
87 impl2_ref.iter().flat_map(|tref| tref.substs.types()),
90 let t1 = fast_reject::simplify_type(tcx, ty1, TreatParams::AsPlaceholders);
91 let t2 = fast_reject::simplify_type(tcx, ty2, TreatParams::AsPlaceholders);
93 if let (Some(t1), Some(t2)) = (t1, t2) {
94 // Simplified successfully
101 // Some types involved are definitely different, so the impls couldn't possibly overlap.
102 debug!("overlapping_impls: fast_reject early-exit");
106 let overlaps = tcx.infer_ctxt().enter(|infcx| {
107 let selcx = &mut SelectionContext::intercrate(&infcx);
108 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).is_some()
115 // In the case where we detect an error, run the check again, but
116 // this time tracking intercrate ambuiguity causes for better
117 // diagnostics. (These take time and can lead to false errors.)
118 tcx.infer_ctxt().enter(|infcx| {
119 let selcx = &mut SelectionContext::intercrate(&infcx);
120 selcx.enable_tracking_intercrate_ambiguity_causes();
122 overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).unwrap(),
127 fn with_fresh_ty_vars<'cx, 'tcx>(
128 selcx: &mut SelectionContext<'cx, 'tcx>,
129 param_env: ty::ParamEnv<'tcx>,
131 ) -> ty::ImplHeader<'tcx> {
132 let tcx = selcx.tcx();
133 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
135 let header = ty::ImplHeader {
137 self_ty: tcx.type_of(impl_def_id).subst(tcx, impl_substs),
138 trait_ref: tcx.impl_trait_ref(impl_def_id).subst(tcx, impl_substs),
139 predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
142 let Normalized { value: mut header, obligations } =
143 traits::normalize(selcx, param_env, ObligationCause::dummy(), header);
145 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
149 /// Can both impl `a` and impl `b` be satisfied by a common type (including
150 /// where-clauses)? If so, returns an `ImplHeader` that unifies the two impls.
151 fn overlap<'cx, 'tcx>(
152 selcx: &mut SelectionContext<'cx, 'tcx>,
153 skip_leak_check: SkipLeakCheck,
156 overlap_mode: OverlapMode,
157 ) -> Option<OverlapResult<'tcx>> {
159 "overlap(impl1_def_id={:?}, impl2_def_id={:?}, overlap_mode={:?})",
160 impl1_def_id, impl2_def_id, overlap_mode
163 selcx.infcx().probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
164 overlap_within_probe(selcx, impl1_def_id, impl2_def_id, overlap_mode, snapshot)
168 fn overlap_within_probe<'cx, 'tcx>(
169 selcx: &mut SelectionContext<'cx, 'tcx>,
172 overlap_mode: OverlapMode,
173 snapshot: &CombinedSnapshot<'_, 'tcx>,
174 ) -> Option<OverlapResult<'tcx>> {
175 let infcx = selcx.infcx();
177 if overlap_mode.use_negative_impl() {
178 if negative_impl(selcx, impl1_def_id, impl2_def_id)
179 || negative_impl(selcx, impl2_def_id, impl1_def_id)
185 // For the purposes of this check, we don't bring any placeholder
186 // types into scope; instead, we replace the generic types with
187 // fresh type variables, and hence we do our evaluations in an
188 // empty environment.
189 let param_env = ty::ParamEnv::empty();
191 let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id);
192 let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id);
194 let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?;
195 debug!("overlap: unification check succeeded");
197 if overlap_mode.use_implicit_negative() {
198 if implicit_negative(selcx, param_env, &impl1_header, impl2_header, obligations) {
203 // We disable the leak when when creating the `snapshot` by using
204 // `infcx.probe_maybe_disable_leak_check`.
205 if infcx.leak_check(true, snapshot).is_err() {
206 debug!("overlap: leak check failed");
210 let intercrate_ambiguity_causes = selcx.take_intercrate_ambiguity_causes();
211 debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes);
213 let involves_placeholder =
214 matches!(selcx.infcx().region_constraints_added_in_snapshot(snapshot), Some(true));
216 let impl_header = selcx.infcx().resolve_vars_if_possible(impl1_header);
217 Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
220 fn equate_impl_headers<'cx, 'tcx>(
221 selcx: &mut SelectionContext<'cx, 'tcx>,
222 impl1_header: &ty::ImplHeader<'tcx>,
223 impl2_header: &ty::ImplHeader<'tcx>,
224 ) -> Option<PredicateObligations<'tcx>> {
225 // Do `a` and `b` unify? If not, no overlap.
226 debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header);
229 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
230 .eq_impl_headers(impl1_header, impl2_header)
231 .map(|infer_ok| infer_ok.obligations)
235 /// Given impl1 and impl2 check if both impls can be satisfied by a common type (including
236 /// where-clauses) If so, return false, otherwise return true, they are disjoint.
237 fn implicit_negative<'cx, 'tcx>(
238 selcx: &mut SelectionContext<'cx, 'tcx>,
239 param_env: ty::ParamEnv<'tcx>,
240 impl1_header: &ty::ImplHeader<'tcx>,
241 impl2_header: ty::ImplHeader<'tcx>,
242 obligations: PredicateObligations<'tcx>,
244 // There's no overlap if obligations are unsatisfiable or if the obligation negated is
247 // For example, given these two impl headers:
249 // `impl<'a> From<&'a str> for Box<dyn Error>`
250 // `impl<E> From<E> for Box<dyn Error> where E: Error`
254 // `Box<dyn Error>: From<&'?a str>`
255 // `Box<dyn Error>: From<?E>`
257 // After equating the two headers:
259 // `Box<dyn Error> = Box<dyn Error>`
260 // So, `?E = &'?a str` and then given the where clause `&'?a str: Error`.
262 // If the obligation `&'?a str: Error` holds, it means that there's overlap. If that doesn't
263 // hold we need to check if `&'?a str: !Error` holds, if doesn't hold there's overlap because
264 // at some point an impl for `&'?a str: Error` could be added.
266 "implicit_negative(impl1_header={:?}, impl2_header={:?}, obligations={:?})",
267 impl1_header, impl2_header, obligations
269 let infcx = selcx.infcx();
270 let opt_failing_obligation = impl1_header
274 .chain(impl2_header.predicates)
275 .map(|p| infcx.resolve_vars_if_possible(p))
276 .map(|p| Obligation {
277 cause: ObligationCause::dummy(),
283 .find(|o| !selcx.predicate_may_hold_fatal(o));
285 if let Some(failing_obligation) = opt_failing_obligation {
286 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
293 /// Given impl1 and impl2 check if both impls are never satisfied by a common type (including
294 /// where-clauses) If so, return true, they are disjoint and false otherwise.
295 fn negative_impl<'cx, 'tcx>(
296 selcx: &mut SelectionContext<'cx, 'tcx>,
300 debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
301 let tcx = selcx.infcx().tcx;
303 // create a parameter environment corresponding to a (placeholder) instantiation of impl1
304 let impl1_env = tcx.param_env(impl1_def_id);
305 let impl1_trait_ref = tcx.impl_trait_ref(impl1_def_id).unwrap();
307 // Create an infcx, taking the predicates of impl1 as assumptions:
308 tcx.infer_ctxt().enter(|infcx| {
309 // Normalize the trait reference. The WF rules ought to ensure
310 // that this always succeeds.
311 let impl1_trait_ref = match traits::fully_normalize(
313 FulfillmentContext::new(),
314 ObligationCause::dummy(),
318 Ok(impl1_trait_ref) => impl1_trait_ref,
320 bug!("failed to fully normalize {:?}: {:?}", impl1_trait_ref, err);
324 // Attempt to prove that impl2 applies, given all of the above.
325 let selcx = &mut SelectionContext::new(&infcx);
326 let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id);
327 let (impl2_trait_ref, obligations) =
328 impl_trait_ref_and_oblig(selcx, impl1_env, impl2_def_id, impl2_substs);
330 // do the impls unify? If not, not disjoint.
331 let Ok(InferOk { obligations: more_obligations, .. }) = infcx
332 .at(&ObligationCause::dummy(), impl1_env)
333 .eq(impl1_trait_ref, impl2_trait_ref)
336 "explicit_disjoint: {:?} does not unify with {:?}",
337 impl1_trait_ref, impl2_trait_ref
342 let opt_failing_obligation = obligations
344 .chain(more_obligations)
345 .find(|o| negative_impl_exists(selcx, impl1_env, impl1_def_id, o));
347 if let Some(failing_obligation) = opt_failing_obligation {
348 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
356 /// Try to prove that a negative impl exist for the given obligation and their super predicates.
357 #[instrument(level = "debug", skip(selcx))]
358 fn negative_impl_exists<'cx, 'tcx>(
359 selcx: &SelectionContext<'cx, 'tcx>,
360 param_env: ty::ParamEnv<'tcx>,
361 region_context: DefId,
362 o: &PredicateObligation<'tcx>,
364 let infcx = &selcx.infcx().fork();
366 if resolve_negative_obligation(infcx, param_env, region_context, o) {
370 // Try to prove a negative obligation exist for super predicates
371 for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) {
372 if resolve_negative_obligation(infcx, param_env, region_context, &o) {
380 #[instrument(level = "debug", skip(infcx))]
381 fn resolve_negative_obligation<'cx, 'tcx>(
382 infcx: &InferCtxt<'cx, 'tcx>,
383 param_env: ty::ParamEnv<'tcx>,
384 region_context: DefId,
385 o: &PredicateObligation<'tcx>,
389 let Some(o) = o.flip_polarity(tcx) else {
393 let mut fulfillment_cx = FulfillmentContext::new();
394 fulfillment_cx.register_predicate_obligation(infcx, o);
396 let errors = fulfillment_cx.select_all_or_error(infcx);
398 if !errors.is_empty() {
402 let mut outlives_env = OutlivesEnvironment::new(param_env);
403 // FIXME -- add "assumed to be well formed" types into the `outlives_env`
405 // "Save" the accumulated implied bounds into the outlives environment
406 // (due to the FIXME above, there aren't any, but this step is still needed).
407 // The "body id" is given as `CRATE_HIR_ID`, which is the same body-id used
408 // by the "dummy" causes elsewhere (body-id is only relevant when checking
409 // function bodies with closures).
410 outlives_env.save_implied_bounds(CRATE_HIR_ID);
412 infcx.process_registered_region_obligations(
413 outlives_env.region_bound_pairs_map(),
414 Some(tcx.lifetimes.re_root_empty),
418 let errors = infcx.resolve_regions(region_context, &outlives_env, RegionckMode::default());
420 if !errors.is_empty() {
427 pub fn trait_ref_is_knowable<'tcx>(
429 trait_ref: ty::TraitRef<'tcx>,
430 ) -> Option<Conflict> {
431 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
432 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
433 // A downstream or cousin crate is allowed to implement some
434 // substitution of this trait-ref.
435 return Some(Conflict::Downstream);
438 if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
439 // This is a local or fundamental trait, so future-compatibility
440 // is no concern. We know that downstream/cousin crates are not
441 // allowed to implement a substitution of this trait ref, which
442 // means impls could only come from dependencies of this crate,
443 // which we already know about.
447 // This is a remote non-fundamental trait, so if another crate
448 // can be the "final owner" of a substitution of this trait-ref,
449 // they are allowed to implement it future-compatibly.
451 // However, if we are a final owner, then nobody else can be,
452 // and if we are an intermediate owner, then we don't care
453 // about future-compatibility, which means that we're OK if
455 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
456 debug!("trait_ref_is_knowable: orphan check passed");
459 debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
460 Some(Conflict::Upstream)
464 pub fn trait_ref_is_local_or_fundamental<'tcx>(
466 trait_ref: ty::TraitRef<'tcx>,
468 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, sym::fundamental)
471 pub enum OrphanCheckErr<'tcx> {
472 NonLocalInputType(Vec<(Ty<'tcx>, bool /* Is this the first input type? */)>),
473 UncoveredTy(Ty<'tcx>, Option<Ty<'tcx>>),
476 /// Checks the coherence orphan rules. `impl_def_id` should be the
477 /// `DefId` of a trait impl. To pass, either the trait must be local, or else
478 /// two conditions must be satisfied:
480 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
481 /// 2. Some local type must appear in `Self`.
482 pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanCheckErr<'_>> {
483 debug!("orphan_check({:?})", impl_def_id);
485 // We only except this routine to be invoked on implementations
486 // of a trait, not inherent implementations.
487 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
488 debug!("orphan_check: trait_ref={:?}", trait_ref);
490 // If the *trait* is local to the crate, ok.
491 if trait_ref.def_id.is_local() {
492 debug!("trait {:?} is local to current crate", trait_ref.def_id);
496 orphan_check_trait_ref(tcx, trait_ref, InCrate::Local)
499 /// Checks whether a trait-ref is potentially implementable by a crate.
501 /// The current rule is that a trait-ref orphan checks in a crate C:
503 /// 1. Order the parameters in the trait-ref in subst order - Self first,
504 /// others linearly (e.g., `<U as Foo<V, W>>` is U < V < W).
505 /// 2. Of these type parameters, there is at least one type parameter
506 /// in which, walking the type as a tree, you can reach a type local
507 /// to C where all types in-between are fundamental types. Call the
508 /// first such parameter the "local key parameter".
509 /// - e.g., `Box<LocalType>` is OK, because you can visit LocalType
510 /// going through `Box`, which is fundamental.
511 /// - similarly, `FundamentalPair<Vec<()>, Box<LocalType>>` is OK for
513 /// - but (knowing that `Vec<T>` is non-fundamental, and assuming it's
514 /// not local), `Vec<LocalType>` is bad, because `Vec<->` is between
515 /// the local type and the type parameter.
516 /// 3. Before this local type, no generic type parameter of the impl must
517 /// be reachable through fundamental types.
518 /// - e.g. `impl<T> Trait<LocalType> for Vec<T>` is fine, as `Vec` is not fundamental.
519 /// - while `impl<T> Trait<LocalType for Box<T>` results in an error, as `T` is
520 /// reachable through the fundamental type `Box`.
521 /// 4. Every type in the local key parameter not known in C, going
522 /// through the parameter's type tree, must appear only as a subtree of
523 /// a type local to C, with only fundamental types between the type
524 /// local to C and the local key parameter.
525 /// - e.g., `Vec<LocalType<T>>>` (or equivalently `Box<Vec<LocalType<T>>>`)
526 /// is bad, because the only local type with `T` as a subtree is
527 /// `LocalType<T>`, and `Vec<->` is between it and the type parameter.
528 /// - similarly, `FundamentalPair<LocalType<T>, T>` is bad, because
529 /// the second occurrence of `T` is not a subtree of *any* local type.
530 /// - however, `LocalType<Vec<T>>` is OK, because `T` is a subtree of
531 /// `LocalType<Vec<T>>`, which is local and has no types between it and
532 /// the type parameter.
534 /// The orphan rules actually serve several different purposes:
536 /// 1. They enable link-safety - i.e., 2 mutually-unknowing crates (where
537 /// every type local to one crate is unknown in the other) can't implement
538 /// the same trait-ref. This follows because it can be seen that no such
539 /// type can orphan-check in 2 such crates.
541 /// To check that a local impl follows the orphan rules, we check it in
542 /// InCrate::Local mode, using type parameters for the "generic" types.
544 /// 2. They ground negative reasoning for coherence. If a user wants to
545 /// write both a conditional blanket impl and a specific impl, we need to
546 /// make sure they do not overlap. For example, if we write
548 /// impl<T> IntoIterator for Vec<T>
549 /// impl<T: Iterator> IntoIterator for T
551 /// We need to be able to prove that `Vec<$0>: !Iterator` for every type $0.
552 /// We can observe that this holds in the current crate, but we need to make
553 /// sure this will also hold in all unknown crates (both "independent" crates,
554 /// which we need for link-safety, and also child crates, because we don't want
555 /// child crates to get error for impl conflicts in a *dependency*).
557 /// For that, we only allow negative reasoning if, for every assignment to the
558 /// inference variables, every unknown crate would get an orphan error if they
559 /// try to implement this trait-ref. To check for this, we use InCrate::Remote
560 /// mode. That is sound because we already know all the impls from known crates.
562 /// 3. For non-`#[fundamental]` traits, they guarantee that parent crates can
563 /// add "non-blanket" impls without breaking negative reasoning in dependent
564 /// crates. This is the "rebalancing coherence" (RFC 1023) restriction.
566 /// For that, we only a allow crate to perform negative reasoning on
567 /// non-local-non-`#[fundamental]` only if there's a local key parameter as per (2).
569 /// Because we never perform negative reasoning generically (coherence does
570 /// not involve type parameters), this can be interpreted as doing the full
571 /// orphan check (using InCrate::Local mode), substituting non-local known
572 /// types for all inference variables.
574 /// This allows for crates to future-compatibly add impls as long as they
575 /// can't apply to types with a key parameter in a child crate - applying
576 /// the rules, this basically means that every type parameter in the impl
577 /// must appear behind a non-fundamental type (because this is not a
578 /// type-system requirement, crate owners might also go for "semantic
579 /// future-compatibility" involving things such as sealed traits, but
580 /// the above requirement is sufficient, and is necessary in "open world"
583 /// Note that this function is never called for types that have both type
584 /// parameters and inference variables.
585 fn orphan_check_trait_ref<'tcx>(
587 trait_ref: ty::TraitRef<'tcx>,
589 ) -> Result<(), OrphanCheckErr<'tcx>> {
590 debug!("orphan_check_trait_ref(trait_ref={:?}, in_crate={:?})", trait_ref, in_crate);
592 if trait_ref.needs_infer() && trait_ref.needs_subst() {
594 "can't orphan check a trait ref with both params and inference variables {:?}",
599 // Given impl<P1..=Pn> Trait<T1..=Tn> for T0, an impl is valid only
600 // if at least one of the following is true:
602 // - Trait is a local trait
603 // (already checked in orphan_check prior to calling this function)
605 // - At least one of the types T0..=Tn must be a local type.
606 // Let Ti be the first such type.
607 // - No uncovered type parameters P1..=Pn may appear in T0..Ti (excluding Ti)
609 fn uncover_fundamental_ty<'tcx>(
614 // FIXME: this is currently somewhat overly complicated,
615 // but fixing this requires a more complicated refactor.
616 if !contained_non_local_types(tcx, ty, in_crate).is_empty() {
617 if let Some(inner_tys) = fundamental_ty_inner_tys(tcx, ty) {
619 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
627 let mut non_local_spans = vec![];
628 for (i, input_ty) in trait_ref
631 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
634 debug!("orphan_check_trait_ref: check ty `{:?}`", input_ty);
635 let non_local_tys = contained_non_local_types(tcx, input_ty, in_crate);
636 if non_local_tys.is_empty() {
637 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
639 } else if let ty::Param(_) = input_ty.kind() {
640 debug!("orphan_check_trait_ref: uncovered ty: `{:?}`", input_ty);
641 let local_type = trait_ref
644 .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate))
645 .find(|ty| ty_is_local_constructor(*ty, in_crate));
647 debug!("orphan_check_trait_ref: uncovered ty local_type: `{:?}`", local_type);
649 return Err(OrphanCheckErr::UncoveredTy(input_ty, local_type));
652 non_local_spans.extend(non_local_tys.into_iter().map(|input_ty| (input_ty, i == 0)));
654 // If we exit above loop, never found a local type.
655 debug!("orphan_check_trait_ref: no local type");
656 Err(OrphanCheckErr::NonLocalInputType(non_local_spans))
659 /// Returns a list of relevant non-local types for `ty`.
661 /// This is just `ty` itself unless `ty` is `#[fundamental]`,
662 /// in which case we recursively look into this type.
664 /// If `ty` is local itself, this method returns an empty `Vec`.
668 /// - `u32` is not local, so this returns `[u32]`.
669 /// - for `Foo<u32>`, where `Foo` is a local type, this returns `[]`.
670 /// - `&mut u32` returns `[u32]`, as `&mut` is a fundamental type, similar to `Box`.
671 /// - `Box<Foo<u32>>` returns `[]`, as `Box` is a fundamental type and `Foo` is local.
672 fn contained_non_local_types<'tcx>(
677 if ty_is_local_constructor(ty, in_crate) {
680 match fundamental_ty_inner_tys(tcx, ty) {
682 inner_tys.flat_map(|ty| contained_non_local_types(tcx, ty, in_crate)).collect()
689 /// For `#[fundamental]` ADTs and `&T` / `&mut T`, returns `Some` with the
690 /// type parameters of the ADT, or `T`, respectively. For non-fundamental
691 /// types, returns `None`.
692 fn fundamental_ty_inner_tys<'tcx>(
695 ) -> Option<impl Iterator<Item = Ty<'tcx>>> {
696 let (first_ty, rest_tys) = match *ty.kind() {
697 ty::Ref(_, ty, _) => (ty, ty::subst::InternalSubsts::empty().types()),
698 ty::Adt(def, substs) if def.is_fundamental() => {
699 let mut types = substs.types();
701 // FIXME(eddyb) actually validate `#[fundamental]` up-front.
705 tcx.def_span(def.did()),
706 "`#[fundamental]` requires at least one type parameter",
712 Some(first_ty) => (first_ty, types),
718 Some(iter::once(first_ty).chain(rest_tys))
721 fn def_id_is_local(def_id: DefId, in_crate: InCrate) -> bool {
723 // The type is local to *this* crate - it will not be
724 // local in any other crate.
725 InCrate::Remote => false,
726 InCrate::Local => def_id.is_local(),
730 fn ty_is_local_constructor(ty: Ty<'_>, in_crate: InCrate) -> bool {
731 debug!("ty_is_local_constructor({:?})", ty);
749 | ty::Projection(..) => false,
751 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match in_crate {
752 InCrate::Local => false,
753 // The inference variable might be unified with a local
754 // type in that remote crate.
755 InCrate::Remote => true,
758 ty::Adt(def, _) => def_id_is_local(def.did(), in_crate),
759 ty::Foreign(did) => def_id_is_local(did, in_crate),
761 // This merits some explanation.
762 // Normally, opaque types are not involed when performing
763 // coherence checking, since it is illegal to directly
764 // implement a trait on an opaque type. However, we might
765 // end up looking at an opaque type during coherence checking
766 // if an opaque type gets used within another type (e.g. as
767 // a type parameter). This requires us to decide whether or
768 // not an opaque type should be considered 'local' or not.
770 // We choose to treat all opaque types as non-local, even
771 // those that appear within the same crate. This seems
772 // somewhat surprising at first, but makes sense when
773 // you consider that opaque types are supposed to hide
774 // the underlying type *within the same crate*. When an
775 // opaque type is used from outside the module
776 // where it is declared, it should be impossible to observe
777 // anything about it other than the traits that it implements.
779 // The alternative would be to look at the underlying type
780 // to determine whether or not the opaque type itself should
781 // be considered local. However, this could make it a breaking change
782 // to switch the underlying ('defining') type from a local type
783 // to a remote type. This would violate the rule that opaque
784 // types should be completely opaque apart from the traits
785 // that they implement, so we don't use this behavior.
790 // Similar to the `Opaque` case (#83613).
794 ty::Dynamic(ref tt, ..) => {
795 if let Some(principal) = tt.principal() {
796 def_id_is_local(principal.def_id(), in_crate)
802 ty::Error(_) => true,
804 ty::Generator(..) | ty::GeneratorWitness(..) => {
805 bug!("ty_is_local invoked on unexpected type: {:?}", ty)